Background and context: Helicopter Emergency Medical Services (HEMS) are highly resource-intensive facilities that are well established as part of trauma systems in many high-income countries. We evaluated the cost-effectiveness of a physician-staffed HEMS intervention in combination with treatment at a major trauma centre versus ground ambulance or indirect transport (via a referral hospital) in New South Wales (NSW), Australia. Methods: Cost and effectiveness estimates were derived from a cohort of trauma patients arriving at St George Hospital in NSW, Australia during an 11-year period. Adjusted estimates of in-hospital mortality were derived using logistic regression and adjusted hospital costs were estimated through a general linear model incorporating a gamma distribution and log link. These estimates along with other assumptions were incorporated into a Markov model with an annual cycle length to estimate a cost per life saved and a cost per life-year saved at one year and over a patient s lifetime respectively in three patient groups (all patients; patients with serious injury [Injury Severity Score > 12]; patients with traumatic brain injury [TBI]). Results: Results showed HEMS to be more costly but more effective at reducing in-hospital mortality leading to a cost per life saved of 1,566,379, 533,781 and 519,787 in all patients, patients with serious injury and patients with TBI respectively. When modelled over a patient s lifetime, the improved mortality associated with HEMS led to a cost per life year saved of 96,524, 50,035 and 49,159 in the three patient groups respectively. Sensitivity analyses revealed a higher probability of HEMS being cost-effective in patients with serious injury and TBI. Conclusion: Our investigation confirms a HEMS intervention is associated with improved mortality in trauma patients, especially in patients with serious injury and TBI. The improved benefit of HEMS in patients with serious injury and TBI leads to improved estimated cost-effectiveness.